1. Field of the Invention
The presently disclosed subject matter relates to a method for producing a lithographic printing plate of a negative type including a polymerizable compound in which an image can be recorded by a laser, and a production apparatus therefor, and particularly relates to a method for producing a lithographic printing plate of a negative type including a polymerizable compound in which after an image is exposed, the image can be developed by an ink and/or dampening water on a printer, and a production apparatus therefor.
2. Description of the Related Art
A lithographic printing plate generally includes a lipophilic image area that receives an ink in a printing process and a hydrophilic non-image area that receives dampening water. Lithography is a method by using the property of water and an oily ink repelling each other. Of the lithographic printing plate, the lipophilic image area and the hydrophilic non-image area respectively work as an ink receiving portion and a dampening water receiving portion (non-ink receiving portion) so that differences in adhesiveness of the ink is produced on the surface of the lithographic printing plate, and the ink is applied only onto the image area. Then, printing is performed by transferring the ink onto a printing medium such as paper.
In order to produce this lithographic printing plate, conventionally, the lithographic printing plate has been obtained as follows: using a lithographic printing plate (PS (Pre-Sensitized) plate) formed by providing an lipophilic photosensitive resin layer (image recording layer) on a hydrophilic support, the PS plate is exposed through a mask such as a lith film, and then, a development treatment by an alkaline developing agent or the like is performed so that the image recording layer corresponding to the image area is left while an unnecessary image recording layer corresponding to the non-image area is dissolved and removed.
Owing to recent advancement in this field, the lithographic printing plate is obtained by a CTP (computer to plate) technique at present. Namely, the lithographic printing plate is obtained by scanning and exposing the lithographic printing plate directly with a laser or laser diode, not through the lith film, and developing the lithographic printing plate. Particularly, lithographic printing plates including a photopolymerizable image recording layer in which a polymerizable compound is polymerized and crosslinked are known. These lithographic printing plates usually have an overcoat layer on the image recording layer in order to block oxygen that inhibits polymerization.
In such a lithographic printing plate having the overcoat layer laminated on the image recording layer, the image recording layer and the overcoat layer are mixed at a stage where the overcoat layer is applied onto the image recording layer and dried, and a component to be contained in the image recording layer moves to the overcoat layer. For this reason, function that the image recording layer should originally have is impaired, causing reduction in both developing properties and print durability. Ink absorbency and print durability are also reduced because the component to be contained in the overcoat layer moves to the image recording layer.
As a method for suppressing the mixing mentioned above, the reduction of the time taken for the overcoat layer to be dried has been performed by reducing an amount of a coating liquid, reinforcing a drying condition, and the like. However, there are restrictions on coating suitability in production, and a sufficient effect has not been obtained.
Problems of the above method for reinforcing drying are that a whole film is densified and that a thermal reaction in an object to be dried is caused over the whole inside of the film.
As mentioned above, a method for efficiently drying and removing a residual solvent in the object to be dried without reducing performance of the object to be dried, and further accelerating densification of the surface and preventing mixing between the respective layers has been strongly desired.
As a drying technique, a method using drying hot air is usually used. On the other hand, various drying methods using hot air containing a solvent vapor are also proposed.
For example, Japanese National Publication of International Patent Application No. 1997-502252 proposes an apparatus that uses a superheated water vapor to continuously dry an object to be dried that contains moisture. Japanese Patent Laid-Open No. 2002-333275 proposes an apparatus that uses a superheated water vapor to perform a drying processing on food products.
Japanese National Publication of International Patent Application No. 2000-516334 and Japanese Patent Laid-Open No. 2002-367950 also propose a vapor dryer for removing waterdrops and other contaminants from a device part with sufficient accuracy by using an inflammable solvent vapor such as isopropyl alcohol or an equivalent solvent having a low ignition point.
Japanese Patent Laid-Open No. 2000-158814 describes a method proposed by Vrentas et al. according to a theoretical analysis as a method for removing a residual solvent of a coating film [J. Appl. Polym. Sci, 30,4499 (1985)]. As a factor that causes difficulties in removing a solvent having a high boiling point and the like that remain in a polymer resin, Vrentas et al. mention that the diffusion coefficient of the solvent in the polymer resin is drastically reduced as the amount of the solvent that remains in the polymer resin is decreased, and that the diffusion coefficient of the solvent in the polymer resin is smaller as the size (mol molecular volume) of the molecule in the solvent itself is larger.
Namely, Vrentas et al. propose that in the polymer resin film in which a slight amount of the solvent having a high boiling point remains, 1) the polymer resin film is exposed to a vapor of a solvent whose mol molecular volume is smaller than that of the solvent having a high boiling point, and heated; and 2) the polymer resin film is removed from the second solvent vapor atmosphere and heated.
Further, Japanese Patent Laid-Open No. 2009-86343 describes drying a photopolymer type photosensitive lithographic printing plate having an overcoat layer (overcoat layer or oxygen permeability adjusting layer) applied on a top layer of the plate by supplying a superheated vapor after the plate is dried in a overcoat layer drying zone, drying the overcoat layer while giving moisture to the overcoat layer, and then controlling the moisture content of the film at cooling and humidity control steps.